Light emitting diodes (LED) are, due to their relatively low energy consumption, long lifetime, and capability of electronic dimming, becoming more and more used in connection with lighting applications. LEDs are successfully used in lighting applications for general illumination such as, wash/flood lights illuminating a wide area or for generating wide light beams e.g. for the entertainment industry.
However, LEDs have not presently been successfully used in connection with light application systems where an image is created and projected towards a target surface. This is especially the case in connection with entertainment lightning, where a high demand for lumen output and high image quality are required. LED projecting systems have not yet been able to fulfill these requirements.
The light in projecting systems is generally collected into an optical gate where the image is generated, and an imaging optical system projects the gate onto a target surface. WO0198706, U.S. Pat. No. 6,227,669 and U.S. Pat. No. 6,402,347 disclose lighting systems comprising a number of LEDs arranged in a plane array where a converging lens is positioned in front of the LEDs in order to focus the light, for instance to illuminate a predetermined area/gate or for coupling the light from the diodes into an optical fiber.
Lighting systems where the light from a number of LEDs are directed towards a common focal point or focusing area are also known. U.S. Pat. No. 6,443,594, U.S. Pat. No. 7,226,185B, EP1710493 use individually refracting means positioned in front of each LED to direct the light form each LED towards a common focal point. JP2006269182 A2, WO0198706, U.S. Pat. No. 5,309,277 tilt the LEDs in relation to the optical axis in order to direct the light form each LED towards a common focal point
The prior art fixtures try to increase the lumen output by adding as many light sources as possible. The consequence is, however, that the efficiency with regard to power consumption versus light output is very low. Furthermore, a large amount of light is lost as the prior art fixtures typically only couple a central part of the light of the light beams through the gate in order to provide a uniform illumination of the gate, which again reduces the efficiency.
Another aspect is the fact the LED generates much heat which can reduce lifetime, efficiency, light output of the LEDs and also cause change in the color of the emitted light. The LED therefore need to be cooled and also kept a constant temperature. The heat increases with the amount of LED and the cooling needs are further increased as more and more LEDs are used. The system where the LED array is mounted in a plane pattern solves the cooling aspect by mounting the LEDs on a planer heat sink. The complexity of the cooling issue is however complicated further in optical systems where the LED are angled in relation to each other.
JP2006269182 discloses a system including LED holding portions on which the LEDs are mounted in such manner that their optical axes are directed to apertures of an aperture portion. The holding portions are embodied as pedestals/turrets and the heat must dissipate through these before it can be led away by a heat sink.
US2008290357 discloses a LED package including a carrier, a pair of conductive wire units, an LED chip, and a control circuit module is provided. The carrier has a carrying portion and a ring frame connected to the periphery of the carrying portion. The carrying portion has a dome-like upper surface and a pair of through holes. The pair of conductive wire units is disposed inside the through holes respectively, and each of the conductive wire units has a conductive wire and an insulating material encapsulating the conductive wire. The LED chip is disposed on the upper surface of the carrier and is electrically connected to the conductive wires. The control circuit module is disposed at a bottom of the carrier and is electrically connected to the conductive wires for controlling the operation of the LED chip.
CN 101832 discloses a light projector where each LED is mounted at the end of a cylinder having radials protruding pins. The cylinders are arranged such the LEDs are arranged in a concave pattern.
US2002/0181231 discloses a lighting system for stage, theatrical and architectural lighting, comprising a frame for supporting a plurality of light emitting diodes. The diodes are mounted to the frame so that each diode is both secured to the frame and also simultaneously positioned wherein each discrete diode light beam is directed to a prescribed remote focal point (target zone) and thereupon directed to a predetermined illumination area. Electrical power for transmitting and controlling electrical voltage to light emitting diodes by electrical circuitry integral with the frame. The frame can be configured as any hollow volume such a cone, a semi-ellipse, and a semi-sphere or can be configured as planar. Flexible blanks having apertures and pads for electrical connections can be used to construct rigid frames. An imaging gate a collimating lens and a focusing lens can be interposed between the frame and the illumination area. The frame can also be a sandwich frame having positive and negative electrically conductive layers interposed between layers of biasable insulating foam.
These systems are complex and expensive to manufacture and the cooling demands are not enough for cooling high power LEDs. The space in a light fixtures is often limited and it is difficult to fit many light sources into prior art fixtures, for instance because the optical components associated with the light sources often take up a lot of space.